1. Field of Invention
The present invention relates to methods for the purification of polymers. More particularly, the present invention relates to methods that utilize supercritical fluid to purify polymers.
2. Description of Related Art
Polymers often include residual solvents, un-reacted monomers, and other impurities subsequent to their manufacture. The presence of such impurities can be problematic in certain applications such as, for example, in the manufacture of pharmaceuticals and other ingested materials.
A variety of methods exist for the purification of polymers. Many of such methods require the use of large quantities of organic solvents. While organic solvents can remove residual monomers and other impurities, they can themselves become contaminants that must also be removed.
In recent years, researchers have experimented with the use of supercritical fluid to extract impurities from polymers. For example, at least one process utilized the ability of supercritical fluid to plasticize some polymers, thereby forming a melt that could be mixed with the supercritical fluid to extract impurities. One drawback of this process was that it required the polymer to plasticize significantly in the presence of supercritical fluid. Many polymers, including many biodegradable polymers, do not plasticize sufficiently to make known supercritical fluid purification techniques viable. In addition, mixing the plasticized polymer with the supercritical fluid is a mechanically intensive process requiring specialized equipment.